The present invention relates to a cassette for a stimulable phosphor sheet, and more particularly to a cassette for storing a stimulable phosphor sheet in a light-shielded condition and loading them into an image recording device or the like, the cassette being arranged to allow a simple mechanism to take the stimulable phosphor sheet out of and/or into the cassette, to be loaded in a variety of selectable positions or attitudes, to take up a small space, and having lock means for securely closing an openable cover of the cassette, the locking means being releasable by pressing forces applied in various different directions.
There has recently been developed and widely used a radiation image recording and reproducing system for producing the radiation-transmitted image of an object using a stimulable phosphor material capable of emitting light upon exposure to stimulating rays. When a certain phosphor is exposed to a radiation such as X-rays, cathode rays, ultraviolet rays, and the like, the phosphor stores a part of the energy of the radiation. When the phosphor exposed to the radiation is subsequently exposed to stimulating rays such as visible light, the phosphor emits light in proportion to the stored energy of the radiation. The phosphor exhibiting such a property is referred to as a "stimulable phosphor".
In the radiation image recording and reproducing system employing such a stimulable phosphor, the radiation image information of an object such as a human body is stored in a sheet having a layer of stimulable phosphor, and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photoelectrically detected to produce an image information signal that is electrically processed for generating image information which is recorded on a recording medium such as a photosensitive material or displayed as a visible image on a CRT or the like.
The radiation image recording and reproducing system includes an image reading device for reading the radiation image recorded on a stimulable phosphor sheet. The image reading device reads the radiation image as follows:
The stimulable phosphor sheet is two-dimensionally scanned by a light beam such as a laser beam, and light emitted from the stimuable phosphor sheet in response to application of the light beam is detected by a light detector such as a photomultiplier or the like, thereby obtaining image information. The two-dimensional scanning of the stimulable phosphor sheet with the light beam is effected by mechanially feeding the stimulable phosphor sheet in one direction for auxiliary scanning, while deflecting the light beam for main scanning in a direction normal to the direction in which the stimulable phosphor sheet is fed.
For recording an image on a stimulable phosphor sheet in an image recording device, an object to be imaged is exposed to radiation, and the stimulable phosphor sheet stored in a cassette is then exposed to the radiation having passed through the object for recording the radiation image on the stimulable phosphor sheet. The stimulable phosphor sheet as it is carried in the cassette is then loaded into the image reading device, in which the stimulable phosphor sheet is taken out of the cassette by a sheet delivery mechanism and delivered to a position where the sheet is scanned by the light beam.
One general cassette construction will be described with reference to FIG. 1 of the accompanying drawings.
A conventional cassette 2 has a casing 6 defining a chamber 4 for storing a stimulable phosphor sheet S therein and a cover 10 angularly movably mounted on one end of the casing 6 by means of a hinge 8.
The cassette 2 is loaded into an image reading device 12, for example, in which the cover 10 is opened by a suction disk or cup 14 to open the chamber 4 into the image reading device 12. Then, a sheet delivery mechanism including a suction cup 16 is operated to attract and pick up the stimulable phosphor sheet S, which is thereafter fed to a scanning reader by a sheet feed mechanism, not shown.
As indicated by the broken lines in FIG. 1, when taking the stimulable phosphor sheet S out of the conventional cassette 2, the stimulable phosphor sheet S must be fanned so as to be prevented from abutting against a front wall 6a of the casing 6 remote from the hinge 8. Therefore, the sheet delivery mechanism is complex since it must displace the suction cup 16 along a path to fan the stimulable phosphor sheet S when it is taken out of the cassette 2.
The cover 10 is turned about one end of the casing 6 for opening the chamber 4 into the image reading device 12. Thus, the image reading device 12 should have a large space therein for allowing opening and closing movement of the cover 10. The image reading device 12 is of a large size since it must store the cassette 2 in its entirety.
For reading information from stimulable phosphor sheets of different sizes, there has to be as many different cassettes 2 as the number of different sheet sizes. Opening and closing the covers 10 of such different cassettes 2 with the same suction cup 14 poses a certain problem. More specifically, when a smaller cover 10 indicated by the dot-and-dash lines in FIG. 1 is to be opened, the cover 10 tends to be largely inclined vertically, making the suction cup 16 ineffective to attract the stimulable phosphor sheet S, which may then drop off the suction cup 16.
In FIG. 1, the cassette 2 is shown as being horizontally loaded into the image reading device 12. However, some image reading devices are arranged such that the cassette 2 should be loaded vertically downwardly in order to meet various demands. The cassette 2 shown in FIG. 1 cannot however be loaded into such image reading device, and hence is less versatile as it can only be used with limited types of image reading devices.
The cassette 2 generally has lock means (not shown) for locking the cover 10 in the closed position so that it will not be opened unless required. If the cover 10 were accidentally opened during delivery of the stimulable phosphor sheet S with a recorded radiation image to the image reading device 12, part of the recorded radiation image would be erased and the image could not correctly be read. Therefore, when carrying the cassette 2, the cover 10 is securely locked on the casing 6 by the non-illustrated lock means. After the cassette 2 has been loaded in the image reading device 2, the lock means is released by unlocking means (not shown) in the image reading device 12, and the cover 10 is opened for removal of the stimulable phosphor sheet S from the casing 6.
The lock means is generally arranged such that it can be released by a pressing force applied in one direction. The unlocking means is positioned in the image reading device 2 in the vicinity of the front end of the cassette 2 where the sheet will be taken out.
As described above, the image reading device 12 accommodates therein the sheet delivery mechanism for taking the stimulable phosphor sheet S from the cassette 2 and the sheet feed mechanism for feeding the stimulable phosphor sheet S to the scanning reader. Therefore, since the unlocking means is positionally limited, the positions where the sheet delivery mechanism and the sheet feed mechanism are located are also limited. As a result, it is difficult to reduce the size of the image reading device 12 in view of the above positional limitations therein. Inasmuch as the unlocking means is limited in position, the position or attitude in which the cassette 2 is loaded cannot freely be selected. As a consequence, the conventional cassette 2 is very poor in versatility and not economic.